This reverts commit 75990b9a8f98ea2d597a31472fb778ec4d55f698.
Reason for revert: Breaks downstream, a use case of having three VP9
encodings, scalability mode only specified on the first layer
(L2T2_KEY) and the other two layers not having a scalability mode but
also being active=false appears to trigger a DCHECK in
call/rtp_video_sender.cc:501. More investigation needed
Original change's description:
> Ship ability to opt-in to VP9/AV1 simulcast.
>
> With this unflagging, an app can opt-in to simulcast when using multiple
> encodings by specifying RTCRtpEncodingParameters.scalabilityMode. This
> ensures backwards-compat with apps relying on 3 encodings to mean SVC
> who traditionally have not specified scalabilityMode.
>
> It fixes the spec/API bug of asking for simulcast and not getting
> simulcast. The field trial exists only as a kill-switch with a TODO to
> remove it.
>
> This ships initial support, however note that the VP9/AV1 simulcast uses
> SimulcastRateAllocator (just like VP8/H264 simulcast). This rate
> allocator uses more kbps than SvcRateAllocator. This should be revisited
> to avoid significant higher bitrates, for example when comparing VP9
> simulcast to VP9 SVC.
>
> Shipping the ability for apps to opt-in makes it easier to exercise
> these new code paths and allows initial feedback from developers, but
> due to the high bitrate (= same bitrate as VP8/H264 simulcast today)
> many apps may find that VP9 SVC is still more beneficial for BW reasons.
>
> Bug: webrtc:14884, webrtc:15005
> Change-Id: I748aae1adb47acc8a6b79b5852cff6aa47a46f5d
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/298046
> Commit-Queue: Henrik Boström <hbos@webrtc.org>
> Reviewed-by: Erik Språng <sprang@webrtc.org>
> Reviewed-by: Evan Shrubsole <eshr@google.com>
> Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
> Cr-Commit-Position: refs/heads/main@{#39601}
Bug: webrtc:14884, webrtc:15005
Change-Id: Ic8f77e6a2971f493d6cd8c23faecd435058a8847
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/298440
Bot-Commit: rubber-stamper@appspot.gserviceaccount.com <rubber-stamper@appspot.gserviceaccount.com>
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Commit-Queue: Henrik Boström <hbos@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#39605}
75ea06f0fa